barcelona:~ # grep -B 2 portage-2.2 /usr/portage/profiles/package.mask
# Zac Medico <zmedico@gentoo.org> (24 Nov 2008)
# In order to ensure that portage-2.1.6 gets sufficient testing,
# portage-2.2 will be masked in package.mask until portage-2.1.6 has
# been marked stable. If you would like to continue using portage-2.2
# then you should unmask it (instead of downgrading to portage-2.1.6).
>=sys-apps/portage-2.2_pre
barcelona:~ #

_________________The manual said "Requires Windows10 or better" so I installed GNU/Linux...

23 Nov 2008; Zac Medico <zmedico@gentoo.org> +portage-2.1.6_rc1.ebuild:
2.1.6_rc1 release. The portage-2.1.6 branch is very close to portage-2.2
except that the unstable features, package sets and preserve-libs, have
been removed. In order to ensure that portage-2.1.6 gets sufficient
testing, portage-2.2 will be masked in package.mask until portage-2.1.6
has been marked stable. If you would like to continue using portage-2.2
then you should unmask it (instead of downgrading to portage-2.1.6).